Printed circuits are widely used in the electronics industry and are commonly manufactured by a "subtractive" process. The conventional subtractive process uses a copper foil bonded to a polymer laminate and includes production of a photographic negative of the circuit layout, photoresist imaging of the circuit on the copper foil, and chemical etching to remove excess copper and leave the copper circuit bonded to the polymer material. Although this multi-step process is effective, it uses organic chemicals and solvents and generates large volumes of spent copper etchant solution that must be recycled. In addition, resolution of the final printed circuit is limited by the photographic negative and photoresist processes as well as by undercutting during the etching step.
With current advances in the electronics industry, there is a demand for ultra-fine electronic circuit layouts that are beyond the capabilities of conventional "subtractive" techniques. Direct laser exposure of photoresist film is a known method for eliminating the photographic negative, but this technique does not address the remaining undesirable characteristics of subtractive processes described above. On the other hand, "additive" electronic circuit fabrication methods have not been widely used because they involve electroless copper plating, which is a very slow process that requires multi-step chemical activation of the polymer support material. Consequently, them is a need for a more efficient electronic circuit fabrication process that improves circuit line resolution, reduces the number of process steps, and reduces or eliminates the generation of environmentally objectionable waste products.